The accuracy of a bow depends strongly on its being properly calibrated and adjusted. In particular, the "nocking point," or point on the bow where the arrow is placed, must be established at an optimum location and marked so that each arrow will be shot from that location. Other adjustments that may be required, depending on the type of bow, include adjustments to cams on compound bows and to the arrow rest on bows. In general, such adjustments are made by shooting several arrows at a target under the same condition and determining the extent to which the resulting pattern is off the desired target location. The knocking point or other adjustable feature is then changed to bring the pattern to the correct location. For effective calibration, this procedure requires that each arrow of a group be fired under precisely reproducible conditions, which result is difficult to obtain by manual shooting owing to the effects of human error or variations in the individual archer's stance.
Various devices relating to mounting and calibration of archery bows are disclosed in prior patents. U.S. Pat. No. 3,651,578 discloses a bow square instrument for calibrating a bow using graduated scales but is not concerned with mounting a bow for shooting a test pattern of errors. U.S. Pat. No. 1,804,450 shows an error testing device wherein a bow is securely mounted to a mechanism that allows for some pivotal movement by adjustment of a turn buckle. The bow in this device is not allowed to rotate freely after an arrow is shot. An archery stand on which a bow is rotatably supported on a horizontal axis is disclosed in U.S. Pat. No. 1,564,089, but this device is concerned only with archery practice and with tuning of bows. A gunsight alignment device providing for rotatable mounting of a weapon on a horizontally disposed pivot pin is disclosed in U.S. Pat. No. 4,621,563. This device allows for limited pivotal movement of the weapon around the pin upon being fired, but such movement is stopped when the weapon contacts a recoil-absorbing spring. None of these patents show a bow calibrating device wherein the bow is rotatably mounted on a horizontal shaft to enable it to be reproducibly brought back to the same position in shooting a test pattern.